Systems and methods for internal surface conditioning assessment in plasma processing equipment

ABSTRACT

In an embodiment, a plasma source includes a first electrode, configured for transfer of one or more plasma source gases through first perforations therein; an insulator, disposed in contact with the first electrode about a periphery of the first electrode; and a second electrode, disposed with a periphery of the second electrode against the insulator such that the first and second electrodes and the insulator define a plasma generation cavity. The second electrode is configured for movement of plasma products from the plasma generation cavity therethrough toward a process chamber. A power supply provides electrical power across the first and second electrodes to ignite a plasma with the one or more plasma source gases in the plasma generation cavity to produce the plasma products. One of the first electrode, the second electrode and the insulator includes a port that provides an optical signal from the plasma.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 15/957,827 filed on Apr. 19, 2018, which is a divisional ofU.S. patent application Ser. No. 14/514,222 filed Oct. 14, 2014, nowU.S. Pat. No. 9,966,240, issued May 8, 2018. The entire contents of bothof the above-identified applications are hereby incorporated byreference in their entireties for all purposes.

TECHNICAL FIELD

The present disclosure applies broadly to the field of plasma processingequipment. More specifically, systems and methods for internal surfaceconditioning assessment of a plasma generator using optical emissionspectroscopy are disclosed.

BACKGROUND

Semiconductor processing often utilizes plasma processing to etch, cleanor deposit material on semiconductor wafers. Predictable andreproducible wafer processing is facilitated by plasma processingparameters that are stable and well controlled. Certain changes toequipment and/or materials involved in plasma processing can temporarilydisrupt stability of plasma processing. This typically occurs when suchchanges affect the surface chemistry of plasma system components, ascompared to the surface chemistry that results from long term use in asingle process. For example, plasma chamber components may requireconditioning upon first-time use, or after the chamber is vented toatmospheric air. In such cases, a plasma process may initially exhibitdeliverables such as etch rate, etch selectivity or deposition rate thatvary but may stabilize over time, for example as surface coatings withinthe process chamber come into equilibrium with the plasma processconditions. Semiconductor manufacturers value rapid stabilization ofprocess conditions and reliable confirmation of process stability, sothat a new or repaired plasma chamber can be placed into use as soon aspossible.

SUMMARY

In an embodiment, a plasma source includes a first electrode, configuredfor transfer of one or more plasma source gases through firstperforations therein; an insulator, disposed in contact with the firstelectrode about a periphery of the first electrode; and a secondelectrode, disposed with a periphery of the second electrode against theinsulator such that the first and second electrodes and the insulatordefine a plasma generation cavity. The second electrode is configuredfor movement of plasma products from the plasma generation cavitytherethrough toward a process chamber. A power supply provideselectrical power across the first and second electrodes to ignite aplasma with the one or more plasma source gases in the plasma generationcavity to produce the plasma products. One of the first electrode, thesecond electrode and the insulator includes a port that provides anoptical signal from the plasma.

In an embodiment, a method assesses surface conditioning of one or moreinternal surfaces of a plasma processing system. The method includesintroducing one or more plasma source gases within a plasma generationcavity of the plasma processing system, the plasma generation cavitybeing bounded at least in part by the one or more internal surfaces, andapplying power across electrodes of the plasma processing system toignite a plasma with the plasma source gases within the plasmageneration cavity. Optical emissions from the plasma are captured withan optical probe that is disposed adjacent the plasma generation cavityand is oriented such that the captured optical emissions are notaffected by interaction of the plasma with a workpiece. One or moreemission peaks of the captured optical emissions are monitored to assessthe surface conditioning of the one or more internal surfaces.

In an embodiment, a plasma processing system includes a remote plasmasystem for ionizing first source gases, and two processing units, eachof the two processing units configured to receive at least the ionizedfirst source gases from the remote processing system, and second sourcegases. Each of the processing units includes a plasma generation chamberthat is bounded by a first planar electrode that is configured fortransfer of the ionized first source gases and the second plasma sourcegases into the plasma generation chamber through first perforationstherein, a second planar electrode that is configured with perforationsconfigured for transfer of plasma products from the plasma generationcavity toward a process chamber, and a ring shaped insulator that isdisposed about and in contact with a periphery of the first electrode,and about and in contact with a periphery of the second electrode. Eachof the processing units further includes a power supply that provideselectrical power across the first and second planar electrodes to ignitea plasma with the ionized first source gases and the second plasmasource gases in the plasma generation cavity, to produce the plasmaproducts. One of the first electrode, the second electrode and theinsulator includes a port that provides an optical signal from theplasma. The port is disposed and oriented such that the optical signalis not influenced by interactions of the plasma products after theytransfer through the second electrode toward the process chamber.

In an embodiment, a method of conditioning internal surfaces of a plasmasource includes flowing first source gases into a plasma generationcavity of the plasma source that is enclosed at least in part by theinternal surfaces. Upon transmitting power into the plasma generationcavity, the first source gases ignite to form a first plasma, producingfirst plasma products, portions of which adhere to the internalsurfaces. The method further includes flowing the first plasma productsout of the plasma generation cavity toward a process chamber where aworkpiece is processed by the first plasma products, flowing secondsource gases into the plasma generation cavity. Upon transmitting powerinto the plasma generation cavity, the second source gases ignite toform a second plasma, producing second plasma products that at leastpartially remove the portions of the first plasma products from theinternal surfaces.

In an embodiment, a method of conditioning one or more internal surfacesof a plasma source after the internal surfaces are exposed toatmospheric air includes flowing at least a hydrogen-containing gas intoa plasma generation cavity of the plasma source, the plasma generationcavity being enclosed at least in part by the one or more internalsurfaces, transmitting power into the plasma generation cavity togenerate a hydrogen-containing plasma, such that H radicals removeexcess oxygen from the internal surfaces, and monitoring emission peaksof the plasma until the emission peaks are stable.

In an embodiment, a method of maintaining stability of a processattribute of a plasma processing system that etches material from wafersincludes generating an etch plasma within the plasma processing systemto create etch plasma products, wherein portions of the etch plasmaproducts adhere to one or more internal surfaces of the plasmaprocessing system, using the etch plasma products to etch the materialfrom the one of the wafers, wherein the portions of the etch plasmaproducts adhered to the one or more internal surfaces affect the processattribute, and generating a conditioning plasma within the plasmaprocessing system to create conditioning plasma products, wherein theconditioning plasma products remove at least some of the etch plasmaproducts adhered to the one or more internal surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be understood by reference to the followingdetailed description taken in conjunction with the drawings brieflydescribed below, wherein like reference numerals are used throughout theseveral drawings to refer to similar components. It is noted that, forpurposes of illustrative clarity, certain elements in the drawings maynot be drawn to scale. In instances where multiple instances of an itemare shown, only some of the instances may be labeled, for clarity ofillustration.

FIG. 1 schematically illustrates major elements of a plasma processingsystem, according to an embodiment.

FIG. 2 schematically illustrates major elements of a plasma processingsystem, in a cross-sectional view, according to an embodiment.

FIG. 3 schematically illustrates details of region A shown in FIG. 2.

FIG. 4 schematically illustrates a top plan view of an exemplary plasmaprocessing system configured to perform various types of processingoperations, according to an embodiment.

FIG. 5 schematically illustrates a pair of processing chambers, disposedas a tandem pair of processing chambers with a tandem tray, according toan embodiment.

FIG. 6 is a flowchart illustrating a method for assessing surfaceconditioning of one or more internal surfaces of a plasma processingsystem, according to an embodiment.

FIGS. 7A and 7B illustrate emission peak information obtained by usingthe method illustrated in FIG. 6, with apparatus like that shown inFIGS. 2 and 3, according to an embodiment.

FIGS. 8A and 8B show plots of emission peak intensities measured in aplasma chamber, over time, for a hydrogen peak and for fluorine peaks,according to an embodiment.

FIG. 9 is a plot of selected ones of the hydrogen emission peaks fromFIG. 8A, and etch rate measurements taken at the corresponding times asthe selected hydrogen emission peaks, according to an embodiment.

FIG. 10A illustrates a yttria surface that is devoid of hydrogen,according to an embodiment.

FIG. 10B illustrates the yttria surface of FIG. 10A, with a few Hradicals adhered to the surface through dangling bonds, according to anembodiment.

FIG. 10C illustrates the yttria surface of FIG. 10B, with F radicalsreacting with some of the H radicals, according to an embodiment.

FIG. 11 is a flowchart that illustrates an etch recipe that alternatesetching on a workpiece, with a conditioning step, according to anembodiment.

FIG. 12A illustrates a yttria surface with a few F atoms adhered to thesurface through dangling bonds, according to an embodiment.

FIG. 12B illustrates a yttria surface undergoing a reaction to removefluorine, according to an embodiment.

FIG. 13A illustrates a yttria surface with adsorbed fluorine, reactingwith moisture to form YO₂ in solid form, and HF which is carried away ingas form, according to an embodiment.

FIG. 13B illustrates the yttria surface of FIG. 13A, with an oxygen atomof YO₂ in solid form reacting with H radicals to form H₂O, which iscarried away in vapor form, according to an embodiment.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates major elements of a plasma processingsystem 100, according to an embodiment. System 100 is depicted as asingle wafer, semiconductor wafer plasma processing system, but it willbe apparent to one skilled in the art that the techniques and principlesherein are applicable to plasma generation systems of any type (e.g.,systems that do not necessarily process wafers or semiconductors).Processing system 100 includes a housing 110 for a wafer interface 115,a user interface 120, a plasma processing unit 130, a controller 140 andone or more power supplies 150. Processing system 100 is supported byvarious utilities that may include gas(es) 155, external power 170,vacuum 160 and optionally others. Internal plumbing and electricalconnections within processing system 100 are not shown, for clarity ofillustration.

Processing system 100 is shown as a so-called indirect, or remote,plasma processing system that generates a plasma in a first location anddirects the plasma and/or plasma products (e.g., ions, molecularfragments, energized species and the like) to a second location whereprocessing occurs. Thus, in FIG. 1, plasma processing unit 130 includesa remote plasma source 132 that supplies plasma and/or plasma productsfor a process chamber 134. Process chamber 134 includes one or morewafer pedestals 135, upon which wafer interface 115 places a workpiece50 (e.g., a semiconductor wafer, but could be a different type ofworkpiece) for processing. In operation, gas(es) 155 are introduced intoplasma source 132 and a radio frequency generator (RF Gen) 165 suppliespower to ignite a plasma within plasma source 132. Plasma and/or plasmaproducts pass from plasma source 132 through a diffuser plate 137 toprocess chamber 134, where workpiece 50 is processed.

Although an indirect plasma processing system is illustrated in FIG. 1and elsewhere in this disclosure, it should be clear to one skilled inthe art that the techniques, apparatus and methods disclosed herein areequally applicable to direct plasma processing systems—e.g., where aplasma is ignited at the location of the workpiece(s). Similarly, inembodiments, the components of processing system 100 may be reorganized,redistributed and/or duplicated, for example: (1) to provide a singleprocessing system with multiple process chambers; (2) to providemultiple remote plasma sources for a single process chamber; (3) toprovide multiple workpiece fixtures (e.g., wafer pedestals 135) within asingle process chamber; (4) to utilize a single remote plasma source tosupply plasma products to multiple process chambers; and/or (5) toprovide plasma and gas sources in serial/parallel combinations such thatvarious source gases may be ionized zero, one, two or more times, andmixed with other source gases before or after they enter a processchamber, and the like.

Plasma-Only Monitoring with OES

FIG. 2 schematically illustrates major elements of a plasma processingsystem 200, in a cross-sectional view, according to an embodiment.Plasma processing system 200 is an example of plasma processing unit130, FIG. 1. Plasma processing system 200 includes a process chamber 205and a plasma source 210. As shown in FIG. 2, plasma source 210introduces gases 155(1) directly, and/or gases 155(2) that are ionizedby an upstream remote plasma source 202, as plasma source gases 212,through an RF electrode 215. RF electrode 215 includes (e.g., iselectrically tied to) a first gas diffuser 220 and a faceplate 225 thatserve to redirect flow of the source gases so that gas flow is uniformacross plasma source 210, as indicated by arrows 231. After flowingthrough face plate 225, an insulator 230 electrically insulates RFelectrode 215 from a diffuser 235 that is held at electrical ground(e.g., diffuser 235 serves as a second electrode counterfacing faceplate 225 of RF electrode 215). Surfaces of RF electrode 215, diffuser235 and insulator 230 define a plasma generation cavity (see plasmageneration cavity 240, FIG. 3) where a plasma 245 is created when thesource gases are present and RF energy is provided through RF electrode215. RF electrode 215 and diffuser 235 may be formed of any conductor,and in embodiments are formed of aluminum (or an aluminum alloy, such asthe known “6061” alloy type). Surfaces of face plate 225 and diffuser235 that face the plasma cavity or are otherwise exposed to reactivegases may be coated with yttria (Y₂O₃) or alumina (Al₂O₃) for resistanceto the reactive gases and plasma products generated in the plasmacavity. Insulator 230 may be any insulator, and in embodiments is formedof ceramic. A region denoted as A in FIG. 2 is shown in greater detailin FIG. 3. Emissions from plasma 245 enter a fiber optic 270 and areanalyzed in an optical emission spectrometer (“OES”) 280, as discussedfurther below.

Plasma products generated in plasma 245 pass through diffuser 235 thatagain helps to promote the uniform distribution of plasma products, andmay assist in electron temperature control. Upon passing throughdiffuser 235, the plasma products pass through a further diffuser 260that promotes uniformity as indicated by small arrows 227, and enterprocess chamber 205 where they interact with workpiece 50, such as asemiconductor wafer, atop wafer pedestal 135. Diffuser 260 includesfurther gas channels 250 that may be used to introduce one or morefurther gases 155(3) to the plasma products as they enter processchamber 205, as indicated by very small arrows 229.

Embodiments herein may be rearranged and may form a variety of shapes.For example, RF electrode 215 and diffuser 235 are substantiallyradially symmetric in the embodiment shown in FIG. 2, and insulator 230is a ring with upper and lower planar surfaces that are disposed againstperipheral areas of face plate 225 and diffuser 235, for an applicationthat processes a circular semiconductor wafer as workpiece 50. However,such features may be of any shape that is consistent with use as aplasma source. Moreover, the exact number and placement of features forintroducing and distributing gases and/or plasma products, such asdiffusers, face plates and the like, may also vary. Also, in a similarmanner to diffuser 260 including gas channels 250 to add gas 155(3) toplasma products from plasma 245 as they enter process chamber 205, othercomponents of plasma processing system 200 may be configured to add ormix gases 155 with other gases and/or plasma products as they make theirway through the system to process chamber 205.

FIG. 3 schematically illustrates details of region A shown in FIG. 2.Face plate 225, insulator 230 and diffuser 235 seal to one another suchthat a plasma generation cavity 240 that is bounded by face plate 225,insulator 230 and diffuser 235 can be evacuated. A facing surface 226 offace plate 225, and/or a facing surface 236 of diffuser 235 may becoated with yttria (Y₂O₃) or alumina (Al₂O₃) for resistance to the gasesand/or plasmas to be used.

When plasma source gases are introduced and electrical power is providedacross face plate 225 and diffuser 235, a plasma 245 can form therein.Insulator 230 forms a radial aperture 237; an optical window 310 sealsto insulator 230 over aperture 237. Optical window 310 is formed ofsapphire, however it is appreciated that other materials for opticalwindow 310 may be selected based on resistance to plasma source gasesand/or plasma products of plasma 245, or transmissivity to opticalemissions, as discussed below. In the embodiment shown in FIG. 3, ano-ring 340 seats in recesses 345 to facilitate sealing optical window310 to insulator 230; however, other sealing geometries and methods maybe utilized. In embodiments, plasma generation cavity 240 is evacuatedsuch that atmospheric pressure (external to plasma generation cavity240) assists in sealing components such as optical window 310 toinsulator 230.

Fiber optic 270 is positioned such that when plasma 245 exists in plasmageneration cavity 240, optical emissions 350 originate in plasma 245,propagate through radial aperture 237 and optical window 310, and intofiber optic 270 to generate an optical signal therein. Fiber optic 270transmits optical emissions 350 to OES 280, FIG. 2. In embodiments,fiber optic 270 is a 400 μm core optical fiber; however, other coresizes and various fiber materials may be selected for transmissivity ofoptical emissions 350 and to manage signal strength within fiber optic270. For example, plasmas 245 that generate low levels of opticalemissions 350 may be monitored utilizing a relatively wide core (e.g.,400 μm) fiber optic 270, while plasmas that generate higher levels ofoptical emissions 350 may be monitored utilizing relatively narrowercores (e.g., 110 μm, 100 μm, 62.5 μm, 50 μm, 9 μm or other core sizes)in order to limit the optical signal reaching OES 280. One or morefilters may be utilized at OES 280 to absorb stray light and/oremissions that are not within a spectral band of interest.

OES 280 analyzes the optical signal received from fiber optic 270 toidentify emission peaks within the signal, including identifyingspecific emission peaks as corresponding to energy transitions ofspecific elements. In some embodiments, spectra and/or informationcharacterizing emission peaks therein may be viewed and/or manipulatedon OES 280. In some of these and in other embodiments, emission peakinformation may be transferred to a computer 290 for analysis,manipulation, storage and/or display.

In embodiments, a fiber optic connector 330 terminates fiber optic 270,and a block 320 positions fiber optic connector 330 with respect tooptical window 310, as shown in FIG. 3. However, this arrangement is byway of example only; other embodiments may provide a custom terminationof fiber optic 270 that does not involve a connector 330, and variousarrangements for positioning fiber optic 270 and/or connector 330 withrespect to window 310 may be implemented in place of block 320. Whenutilized, block 320 may extend in and out of the cross-sectional planeshown in FIG. 3 to form attachment regions, and may fasten to insulator230 using fasteners such as screws in such regions. Block 320 and/orscrews that attach block 320 to insulator 230 are advantageouslyfabricated of insulative materials such as plastic or ceramic, tomitigate any possibility of electrical arcing to or from face plate 225and diffuser 235, and/or other structures.

It is appreciated that aperture 237 and optical window 310, at least,function as a port for providing an optical signal from plasma 245 thatcan be utilized to monitor aspects of plasma source 210. It is alsoappreciated that such port may be provided at a variety of locationswithin a plasma source. For example, generally speaking, a capacitivelycoupled plasma source will include at least two electrodes separated byan insulator; a port such as described above could be disposed with anyof the electrodes or the insulator. Similarly, an inductively coupledplasma source (or any other type of plasma source) could include a portdisposed with any vessel in which the plasma is initially generated.Materials and/or locations of such ports should be selected so as not todisrupt electrical or magnetic circuits that are important to the plasmasource (e.g., to mitigate arcing and/or disturbance of magnetic fielddistributions, for inductively coupled plasma sources).

Returning to FIG. 2, optical monitoring of plasma at the place where itis generated in a remote plasma source provides unique benefits. Becauseplasma 245 is monitored upstream of its interactions with a workpiece 50(e.g., a wafer), the monitoring provides characterization of the plasmasource alone, which may be contrasted or correlated with effectsproduced by interaction with the workpiece. That is, the geometry ofinsulator 230 and radial aperture 237 will tend to provide fiber optic270 with an effective “view” that is limited to optical emissionsresulting from plasma 245 and interactions of those emissions withadjacent surfaces, rather than emissions resulting from downstreaminteractions and/or direct views of surfaces within a process chamber.Monitoring of a plasma at a location where it has not yet had anopportunity to interact with a workpiece is called “upstream” plasmamonitoring herein.

By way of contrast, optical monitoring of workpieces themselves, and/orplasma interaction with such workpieces, may be used to monitor certainplasma effects on the workpiece, but are susceptible to influence by theworkpiece. Workpiece-affected plasma characteristics, including opticalemissions captured with optical probes, are sometimes utilized todetermine a plasma processing endpoint, that is, to identify a time atwhich processing is essentially complete such that some aspect of theplasma process can be turned off. For example, interaction with aworkpiece can affect a plasma by releasing reaction products from theworkpiece, and/or the workpiece can deplete reactive species from theplasma. When reaction products from the workpiece are no longerdetected, it may signify that a layer to be etched has “cleared” suchthat etch gases and/or RF energy can be turned off. However, suchoptical probes are situated where the optical emissions that arecaptured are affected by the workpiece.

Both workpiece-affected and upstream plasma monitoring can be usefultools in determining whether variations in processed workpieces are dueto variations in a plasma as generated, or due to variations present inthe workpieces before they interact with the plasma. In certainembodiments herein, stable process results correlate strongly withupstream plasma monitoring results. Specifically, process results havebeen found to correlate with certain emission peaks measured with theapparatus described in connection with FIGS. 2 and 3. When strongcorrelations between upstream monitoring of plasma emission peaks andprocess results can be identified, it becomes possible, in embodiments,to run conditioning process cycles without exposing valuable workpiecesto risk until those emission peaks are observed to be stable. Once theemission peaks are stable, workpieces can be processed in confidencethat the process results will be as expected.

Stability in emission peaks obtained from upstream monitoring canindicate equilibrium in reactions between the generated plasma andadjacent surfaces. For example, certain surfaces of electrodes,diffusers and the like may interact with a plasma to slowly give off, orabsorb, certain elements that are important to process results, suchthat the resulting plasma process will not be stable until the surfacesare in equilibrium with the plasma. In embodiments, electrodes,diffusers and the like may be coated with refractory materials such asyttria (Y₂O₃) or alumina (Al₂O₃) for resistance to the gases and/orplasmas to be used. These materials can interact with plasma productssuch as free hydrogen, such that plasmas generated around such surfacesmay not be stable until the surfaces are either saturated orsubstantially depleted of hydrogen. In either case, emission peaksgenerated through upstream plasma monitoring can be useful for assessingplasma stability.

Accurately identifying when plasma equipment is running a stable processis valuable in the semiconductor industry. Semiconductor processing ischaracterized both by unusable equipment having high cost and workpieceshaving high value that is at risk if processing is not optimal. Forexample, a single plasma processing system may represent hundreds ofthousands, or a few million dollars of capital investment, with outputof a multimillion dollar wafer fabrication area being dependent on onlya few of such systems. Yet, a single semiconductor wafer may accruehundreds or thousands of dollars of invested processing costs, and apiece of plasma equipment might process tens of such wafers per hour.Thus the financial costs of equipment downtime, or of utilizingequipment that is not operating correctly, are both quite high.

FIG. 4 schematically illustrates a top plan view of an exemplary plasmaprocessing system 400A configured to perform various types of processingoperations. In FIG. 4, a pair of front opening unified pods (“FOUPs”) orholding chambers 402 supply workpieces (e.g., semiconductor wafers) of avariety of sizes that are received by robotic arms 404 and placed intolow pressure loading chambers 406 before being placed into one of theworkpiece processing chambers 408 a-f, positioned on tandem trays 409a-c. In alternative arrangements, the system 400A may have additionalFOUPs, and may for example have 3, 4, 5, 6, etc. or more FOUPs. Theprocess chambers may include any of the chambers as described elsewherein this disclosure. Robotic arms 411 may be used to transport theworkpieces from the loading chambers 406 to the workpiece processingchambers 408 a-f and back through a transfer chamber 410. Two loadingchambers 406 are illustrated, but the system may include a plurality ofloading chambers that are each configured to receive workpieces into avacuum environment for processing. Process chambers 408 and transferchamber 410 may be maintained in an inert environment, such as withnitrogen purging, which may be continuously flowed through each of thechambers to maintain the inert atmosphere. The loading chamber 406 maysimilarly be configured to be purged with nitrogen after receiving aworkpiece in order to provide the workpiece to the process sections in asimilar environment.

Each workpiece processing chamber 408 a-f, can be outfitted to performone or more workpiece processing operations including dry etchprocesses, cyclical layer deposition (CLD), atomic layer deposition(ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD),etch, pre-clean, degas, orientation, and other workpiece processes. In adisclosed embodiment, for example, the system may include at least twopairs of tandem processing chambers. A first of the at least two pairsof tandem processing chambers may be configured to perform a siliconoxide etching operation, and the second of the at least two pairs oftandem processing chambers may be configured to perform a silicon orsilicon nitride etching operation. A given pair of processing chambers408 may both be configured for a specific process step, and monitoredusing methods described herein to ensure that the processing provided byeach of the pair of chambers matches closely to the other. Whenconfigured in pairs, each processing chamber 408 may be coupledindependently with support equipment such as gas supplies, RFgenerators, remote plasma generators and the like, but in embodiments,adjacent processing chambers 408 share connections with certain suchsupport equipment.

The workpiece processing chambers 408 a-f may include one or more systemcomponents for depositing, annealing, curing and/or etching a film onthe workpiece. In one configuration, two pairs of the processingchambers, e.g., 408 c-d and 408 e-f, may be used to perform a firstetching operation on the workpiece, and the third pair of processingchambers, e.g., 408 a-b, may be used to perform a second etchingoperation on the workpiece. In another configuration, all three pairs ofchambers, e.g., 408 a-f, may be configured to etch a dielectric film onthe workpiece. In still another configuration, a first pair of theprocessing chambers, e.g., 408 a-b, may perform a deposition operation,such as depositing a flowable film, a native oxide, or additionalmaterials. A second pair of the processing chambers, e.g., 408 c-d, mayperform a first etching operation, and the third pair of the processingchambers, e.g., 408 e-f, may perform a second etching operation. Any oneor more of the processes described may be alternatively carried out inchambers separated from the fabrication system shown in differentembodiments. It will be appreciated that additional configurations ofdeposition, etching, annealing, and curing chambers for films arecontemplated by system 400A.

The processing chambers herein may perform any number of processes, suchas a PVD, a CVD (e.g., dielectric CVD, MCVD, MOCVD, EPI), an ALD, adecoupled plasma nitridation (DPN), a rapid thermal processing (RTP), ora dry-etch process to form various device features on a surface of aworkpiece. The various device features may include, but are not limitedto the formation and/or etching of interlayer dielectric layers, gatedielectric layers, polycrystalline silicon (“polysilicon”) layers orgates, forming vias and trenches, planarization steps, and depositingcontact or via level interconnects. In one embodiment, certain positionsmay be occupied by service chambers that are adapted for degassing,orientation, cool down, analysis and the like. For example, one chambermay include a metrology chamber that is adapted to perform apreparation/analysis step and/or a post-processing/analysis step toanalyze a property of the workpiece before or after performing aprocessing step in a processing sequence. In general, the properties ofthe workpiece that can be measured in the metrology chamber may include,but are not limited to, a measurement of intrinsic or extrinsic stressin one or more layers deposited on a surface of the workpiece, filmcomposition of one or more deposited layers, a number of particles onthe surface of the workpiece, and/or a thickness of one or more layersfound on the surface of the workpiece. Data collected from the metrologychamber may then be used by a system controller to adjust one or moreprocess variables in one or more of the processing steps to producefavorable process results on subsequently processed workpieces.

System 400A may include additional chambers 405, 407 on opposite sidesof an interface section 403. The interface section 403 may include atleast two interface transfer devices, such as robot arms 404, that areconfigured to deliver workpieces between FOUPs 402 and the plurality ofloading chambers 406. The holding chambers 402 may be coupled with theinterface section 403 at a first location of the interface section, andthe loading chambers may be coupled with the interface section 403 at asecond location of the interface section 403 that is opposite theplurality of holding chambers 402. The additional chambers may beaccessed by interface robot arms 404, and may be configured fortransferring workpieces through interface section 403. For example,chamber 405 may provide, for example, wet etching capabilities and maybe accessed by interface robot arm 404 a through the side of interfacesection 403. The wet station may be coupled with interface section 403at a third location of interface section 403 between the first locationand second location of the interface section. In disclosed embodimentsthe third location may be adjacent to either of the first and secondlocations of interface section 403. Additionally, chamber 407 mayprovide, for example, additional storage and may be accessed byinterface robot arm 404 b through the opposite side of interface section403 from chamber 405. Chamber 407 may be coupled with interface section403 at a fourth location of the interface section opposite the thirdlocation. Interface section 403 may include additional structures forallowing the transfer of workpieces between the robot arms 404,including transfer section 412 positioned between the robot arms 404.Transfer section 412 may be configured to hold one or more workpieces,and may be configured to hold 2, 5, 10, 15, 20, 25, 50, 100 etc. or moreworkpieces at any given time for delivery for processing. A transfersection 412 may include additional capabilities including cooling of theworkpieces below atmospheric conditions as well as atmospheric cleaningof the wafers, for example. The system 400A may additionally include gasdelivery systems and system controllers (not shown) for providingprecursors and instructions for performing a variety of processingoperations.

FIG. 5 is a schematic side view illustrating a pair of processingchambers 408 g and 408 h, disposed as a tandem pair of processingchambers with a tandem tray 409. Each processing chamber 408 g, 408 h isshown in simplified form relative to the features shown in FIGS. 2 and3, but should be understood to include the same components. Componentsthat are the same for both processing chambers 408 g, 408 h include RFelectrode 215, insulator 230 and diffuser 260. In the embodiment shownin FIG. 5, a remote plasma source (RPS) 202 is a shared resource forboth processing chambers 408 g, 408 h. RPS 202 receives input processgas(es) 155(2); further input process gas(es) 155(1) may be mixed withplasma products from RPS 202 and provided to processing chambers 408 gand 408 h, as shown. Processing chambers 408 g and 408 h may receivefurther process gas(es) 155(3) and 155(4), and may be respectivelyenergized by RF power supplies 510(1) and 510(2). Gases 155(3) and155(4), and RF power supplies 510(1) and 510(2) are independentlycontrollable for processing chambers 408 g and 408 h. That is, it ispossible to provide different gas(es) and flow rates through the gasconnections, and/or operate one of RF power supplies 510(1) and 510(2)at a time, or operate power supplies 510(1) and 510(2) at differentpower levels. The ability to control gases 155(3) and 155(4) and RFpower supplies 510(1) and 510(2) independently is an important featurefor processing and chamber conditioning purposes, as discussed furtherbelow.

FIG. 6 is a flowchart illustrating a method 600 for assessing surfaceconditioning of one or more internal surfaces of a plasma processingsystem. Method 600 begins with introducing one or more plasma sourcegases within a plasma generation cavity of the plasma system (610). Thecavity is bounded at least in part by the internal surfaces. Forexample, surface conditioning of surfaces of face plate 225 (part of RFelectrode 215) and diffuser 235 of plasma processing system 200, FIG. 2,can be assessed. In this case, as shown in FIGS. 2 and 3, plasmageneration cavity 240 is bounded at least in part by internal surfaces226 and 236 (labeled only in FIG. 3). Plasma source gases 212 can beintroduced, as shown in FIG. 2. Method 600 proceeds to apply poweracross electrodes of the plasma apparatus to ignite a plasma with theplasma source gases within the plasma generation cavity (620). Forexample, RF power may be provided across RF electrode 215 (includingface plate 225) and diffuser 235, igniting plasma 245 within plasmageneration cavity 240, as shown in FIGS. 2 and 3. Method 600 furtherproceeds to capture optical emissions from the plasma with an opticalprobe that is disposed adjacent the plasma generation cavity (630). Theoptical probe is oriented such that the captured optical emissions arenot affected by interaction of the plasma with a workpiece. An exampleof capturing the optical emissions is receiving optical emissions 350through optical window 310 into fiber optic 270, FIG. 3. Method 600further proceeds to monitor one or more emission peaks of the capturedoptical emissions to assess conditioning of the one or more internalsurfaces (640). An example of monitoring one or more emission peaks ofthe captured optical emissions is optical emission spectrometer 280,FIG. 2, analyzing the optical signal captured into fiber optic 270 toidentify emission peaks, and utilizing information of the emission peaksto assess conditioning of the surfaces.

In embodiments, the emission peak information may be evaluated by ahuman. Alternatively, OES 280 and/or computer 290 may generate stabilitymetrics from the information. For example, a process sequence(hereinafter referred to as a “recipe,” which could be an “etch recipe,”a “deposition recipe,” a “conditioning recipe” or other types, dependingon the processing performed by the process sequence) may include a stepduring which OES 280 measures optical emissions and creates informationabout emission peaks. The information may include what peaks (e.g.,spectral wavelengths or wavelength bands) are detected, and/or intensityof one or more detected emission peaks. The information may be furtherprocessed by assessing trends such as changes in emission peak intensityover recipe cycles, or by statistics such as calculating mean, median,standard deviation and the like over groups of recipe cycles.

FIGS. 7A and 7B illustrate emission peak information obtained by usingmethod 600 with apparatus like that shown in FIGS. 2 and 3, for a plasmagenerated for a polysilicon etch process. Optical emissions of a plasmawere measured and displayed using an OES 280 that automaticallyidentifies known emission peaks. In the examples shown in FIGS. 7A and7B, peaks corresponding to He, N₂, H and F are labeled. The verticalaxis of each of FIGS. 7A and 7B is in arbitrary units (AU) of signalintensity. Emission peak information such as intensities of individualpeaks, ratios of peak intensities, and other statistics can be utilizedto assess conditions of surfaces adjacent to the plasma that ismeasured.

An example of assessing conditions of surfaces adjacent to a plasma isillustrated in FIGS. 8A, 8B and 9. FIGS. 8A and 8B show plots ofemission peak intensities measured in a chamber generating a plasma fora polysilicon etch process, over time, for a hydrogen peak (FIG. 8A,data 700) and for fluorine peaks (FIG. 8B, data 710, 720). Both FIGS. 8Aand 8B show data from the same plasma chamber at the same time, startingafter an equipment intervention was performed, during which the chamberwas open to atmospheric air for a time. Conditioning cycles were run,and etch rate of a plasma process on polysilicon was periodicallymeasured. The time period represented in FIGS. 8A and 8B isapproximately 18 hours.

In FIG. 8A, it can be seen in data 700 that the hydrogen peak intensitygradually increases over time. In FIG. 8B, it can be seen in data 710and 720 that the fluorine peak intensity increases slightly within aboutthe first two hours, but then remains about constant.

FIG. 9 is a plot of selected ones of the hydrogen emission peaks fromFIG. 8A, and polysilicon etch rate measurements taken at timescorresponding to the selected hydrogen emission peaks. The diamondshaped points in FIG. 9 are the H emission peak intensities, correlatedto the left hand vertical axis; the square shaped points are thepolysilicon etch rate measurements, correlated to the right handvertical axis; time is on the horizontal axis. It can be seen that thepolysilicon etch rate varies similarly, over time, as the H emissionpeak intensities. A trend analysis of etch rate against H emission peakintensity revealed a correlation coefficient r² of 0.97 for therelationship of etch rate to H emission peak intensity. Therefore, the Hemission peak intensity strongly predicted etch rate, such thatstability in the H peak can be used as an indicator of equipmentstability. Reaction mechanisms underlying these phenomena, andconditioning plasma recipes to improve etch process stability are nowexplained.

Si Etch and Chamber Conditioning Chemistry and Recipes

A polysilicon (Si) etch process associated with the data in FIGS. 7A,7B, 8A, 8B and 9 proceeds according to the reaction:2NF₃+H₂+Si(s)→2HF+SiF₄+N₂  Reaction (1)wherein all of the species noted are in gas form except for solidsmarked with (s). In reaction (1), polysilicon is the solid Si and isprovided as a film on workpiece 50, a semiconductor wafer; NF₃ and H₂are provided as gases and/or plasma products (e.g., generated in plasma245, see FIG. 2). Certain intermediate steps are omitted in reaction(1); for example the plasma products generated in plasma 245 includefree H radicals.

Free H radicals in plasma 245 can adhere to yttria surfaces of faceplate 225 and diffuser 235. Although the full stoichiometry of yttria isY₂O₃, a yttria surface typically presents YO at an outermost part of thesurface, with which an H radical can form a dangling bond:H+YO→YOH  Reaction (2)

FIG. 10A illustrates a yttria surface 750(1) that is devoid of hydrogen,while FIG. 10B illustrates the same surface with a few H radicalsadhered to the surface through dangling bonds, forming surface 750(2).Because surface 750(1) reacts with a fraction of H radicals in plasma245, the H radical concentration passing through diffuser 235 isdepleted. As more and more H radicals bond to the surface to formsurface 750(2), the rate of H radical depletion is reduced, causing theH radical concentration reaching workpiece 50 to increase, leading to anetch rate increase as per reaction (1).

While it may be possible in some cases to saturate a yttria surface withhydrogen to stabilize etch rate, it can be very time consuming to do so,and certain adverse process characteristics may result. An alternativeis to at least remove a portion of the hydrogen and leave the surface atleast substantially hydrogen free, such that the etch rate is at leastpredictable. Free fluorine radicals can scavenge the hydrogen, accordingto the reaction:F+YOH(s)→YO(s)+HF  Reaction (3)

Free F radicals can be supplied to perform reaction (3) through aconditioning plasma step. In an embodiment, the conditioning plasma stepgenerates a plasma from NF₃. While other F-containing gases could beused for the conditioning step, NF₃ may be advantageously used if it isalready plumbed into the plasma processing equipment for a Si etch step.FIG. 10C illustrates a yttria surface 750(3) reacting with free Fradicals to strip some of the H, as compared with yttria surface 750(2).To reestablish etch rate stability in a chamber having excess H onyttria surfaces, it is not necessary to remove all of the H. Tostabilize etch rate within a reasonable amount of time, it may besufficient to remove about as much H with a conditioning recipe, as isadded in an etch step. This can be done by performing the conditioningplasma in between successive workpiece processing steps. When apolysilicon etch process and the wafers being etched are stable, aconditioning recipe can be run as a timed NF₃ plasma step. It may alsobe desirable to monitor the H emission peak during an NF₃ plasma todetermine a suitable time to stop the plasma (e.g., based on the Hemission peak falling to a particular value). The H peak could bemonitored during the conditioning NF₃ plasma step, or the H peak couldbe monitored during the etch step and used to adjust one or moreparameters of the subsequent conditioning plasma step, such as gasflows, pressure, RF power or time during the conditioning plasma step.

FIG. 11 is a flowchart that illustrates an etch recipe 800 thatalternates etching on a workpiece, with a conditioning step. Etch recipe800 is generalized in that a variety of etch and conditioning steps canbe used, as now discussed.

Recipe 800 begins by loading a workpiece to be etched, in step 810. Anexample of step 810 is loading a semiconductor wafer with Si to beetched into plasma processing system 200, FIG. 2. Next, in step 820 theetch is performed. An example of step 820 is etching Si with NF₃+H₂,according to reaction (1) above. During step 820, surfaces of the plasmaprocessing system may be degraded by plasma products and/or gases usedfor the etching. An example of such degradation is H radicals formingdangling bonds to yttria surfaces, according to reaction (2) above. Anoptional step 825 of monitoring an emission peak in the plasma using OESmay be performed concurrently with step 820, utilizing the apparatusdiscussed above (see FIGS. 2 and 3). The emission peak information maybe used as an equipment monitor to confirm that the chamber condition,and thus the etch rate, is stable from workpiece to workpiece, and/or toadjust time of the conditioning step (step 840). In an example of step825, H emission peak information is monitored, recorded and/or used todetermine when to stop later step 840. After step 820, the workpiece maybe unloaded in an optional step 830; alternatively, step 830 may beomitted if the processing described in step 840 will not impact theworkpiece. Omission of step 830 may lead to recipe 800 running a bitquicker than if step 830 is included, because of the time typicallyrequired to evacuate the process chamber for unloading, and toreestablish gas flows for the plasma generated in step 840.

Next, in step 840 a conditioning plasma is performed. An example of step840 is conditioning the plasma generation chamber with an NF₃ plasma toremove H from the yttria surfaces, according to reaction (3) above. Anoptional step 845 of monitoring an emission peak in the plasma using OESmay be performed concurrently with step 840. An example of optional step845 is monitoring an H emission peak in the plasma using OES. Theemission peak information can be used to adjust time of step 840, and/oras an equipment monitor to confirm that the chamber condition, and thusthe etch rate, is consistent after each repetition of recipe 800.

Considering recipe 800 in the context of FIGS. 4 and 5, it isappreciated that when a pair of processing chambers 408 are dedicated tosimilar processes, etch step 820 and/or conditioning plasma step 840could be adjusted specifically for each of the pair of chambers 408, andthis tailoring may be based on emission peak monitoring. For example,recipe 800 could monitor an emission peak during either etch step 820 orconditioning plasma step 840, and adjust parameters such as gas flows,pressures, RF power and/or time of conditioning step 840 across the twochambers to keep performance of the two chambers tightly matched at etchstep 820.

Si₃N₄ Etch and Chamber Conditioning Chemistry and Recipes

An exemplary silicon nitride (Si₃N₄, sometimes referred to herein simplyas “nitride”) etch process proceeds according to the reaction:4NF₃+Si₃N₄→3SiF₄+4N₂  Reaction (4)

In reaction (4), Si3N4 is provided as a film on workpiece 50, asemiconductor wafer; plasma products of NF₃ are provided to theworkpiece (e.g., generated in plasma 245, see FIG. 2). Certainintermediate steps are omitted in reaction (1); for example the plasmaproducts generated in plasma 245 include free F radicals.

Free F radicals in plasma 245 can adhere to yttria surfaces of faceplate 225 and diffuser 235, forming dangling bonds:F+YO→YOF  Reaction (5)

FIG. 12A illustrates a yttria surface 900(1) with a few F radicalsadhered to the surface through dangling bonds. The F radicals can desorbfrom the yttria surface during etching, and cause degraded etchselectivity of the nitride etch with respect to silicon dioxide (SiO₂,sometimes referred to herein simply as “oxide”). In at least someprocessing scenarios, nitride etches need to be selective to nitrideover oxide, that is, they should etch nitride at a much higher rate thanthey etch oxide. Somewhat analogously to the Si etch discussed above,the oxide etch rate will climb, and thus the selectivity will degrade,as the F on the chamber walls increases.

Another application of recipe 800 provides a way to ameliorate thisissue. Free H radicals can scavenge F from the chamber walls, much likethe reverse of reaction (3) above:H+YOF(s)→YO(s)+HF  Reaction (6)

FIG. 12B illustrates yttria surface 900(2) undergoing reaction (6). Likethe Si etch and adsorbed H discussed above, it may not be necessary toremove all of the F from yttria surface 900(2), but it may be helpful toscavenge F just down to a low enough level that poor selectivity tooxide ceases to be an issue.

Therefore, in one embodiment, recipe 800 can be run using NF₃ in etchstep 820 to drive reaction (4), etching Si₃N₄, and using ahydrogen-containing gas such as NH₃ and/or H₂ in conditioning step 840,to generate free H radicals to drive reaction (6). In this case, Femission peaks could be monitored in step 845 to ensure consistency ofthe plasma chamber condition at the end of step 840, before the nextrecipe cycle when etch step 820 will be performed. It may also bepossible to run conditioning step 840 longer to drive adsorbed F toextremely low levels if the next workpiece(s) to be processed wouldbenefit from an extremely high selectivity etch. Also, in thisembodiment, it may be possible to run recipe 800 without step 830, ifthe workpiece would not be adversely affected by hydrogen plasmaproducts with traces of HF.

Chamber Conditioning Chemistry and Recipes—Adsorbed Oxygen from Moisture

When plasma equipment is newly built or exposed to atmospheric airduring maintenance work, moisture can react with fluorinated yttriasurfaces such that extra oxygen adheres to such surfaces. The oxygenadsorption process proceeds according to the reaction:2YOF+H₂O→YO+YO₂+2HF  Reaction (7)which is illustrated in FIG. 13A, showing surface 950(1) with adsorbedfluorine, reacting to form YO₂ in solid form, and HF which is carriedaway in gas form. The extra O on the yttria surface may react withprocessing plasmas and/or interfere with intended reactions of suchplasmas.

Like reducing adsorbed F, YO₂ can be treated with a hydrogen-containinggas such as NH₃ and/or H₂ to form a plasma that removes the extraoxygen, leaving the yttria in its native state. The plasma produces freeH radicals as plasma products, which react according to:2H+YO₂(s)→YO(s)+H₂O  Reaction (8)

FIG. 13B shows surface 960(1) with an instance of YO₂ in solid form. Asshown in FIG. 13B, H radicals react with an oxygen atom of the YO₂ toform H₂O, which is carried away in vapor form from the resulting surface960(2). Like the Si etch case discussed above, an H emission peak couldbe monitored for stability of plasma generation cavity surfaces, aconstant H peak signifying a stable YO surface. Also, the H containingplasma may leave H adhered to YO surfaces, as discussed in connectionwith FIG. 10B above. Therefore, depending on the processing that isintended for the plasma processing equipment, the chamber could befurther conditioned with plasma generated from a fluorine-containing gas(e.g., NF₃) to reduce hydrogen that may adhere to YO surfaces during theH radical treatment, as shown in FIG. 10C. The conditioning treatmentwould amount to simply running step 840 of recipe 800 (FIG. 11),optionally monitoring one or more emission peak(s) with an opticalemission spectrometer (step 845) until the peaks are stable.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Additionally, a number of well-known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent invention. Accordingly, the above description should not betaken as limiting the scope of the invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” or “a recipe”includes a plurality of such processes and recipes, reference to “theelectrode” includes reference to one or more electrodes and equivalentsthereof known to those skilled in the art, and so forth. Also, the words“comprise,” “comprising,” “include,” “including,” and “includes” whenused in this specification and in the following claims are intended tospecify the presence of stated features, integers, components, or steps,but they do not preclude the presence or addition of one or more otherfeatures, integers, components, steps, acts, or groups.

We claim:
 1. A plasma processing system, comprising: a remote plasmasystem for ionizing first source gases; and two processing units, eachof the two processing units configured to receive at least the ionizedfirst source gases from the remote processing system, and second sourcegases; each of the processing units comprising: a plasma generationchamber that is bounded by: a first planar electrode that is configuredfor transfer of the ionized first source gases and the second plasmasource gases into the plasma generation chamber through firstperforations therein, a second planar electrode that is configured withperforations configured for transfer of plasma products from the plasmageneration chamber toward a process chamber, and a ring shaped insulatorthat is disposed about and in contact with a periphery of the firstplanar electrode, and about and in contact with a periphery of thesecond planar electrode; and a power supply that provides electricalpower across the first and second planar electrodes to ignite a plasmawith the ionized first source gases and the second plasma source gasesin the plasma generation chamber, to produce the plasma products;wherein: one of the first planar electrode, the second planar electrodeand the ring shaped insulator includes a port that provides an opticalsignal from the plasma, the port being disposed and oriented such thatthe optical signal is not influenced by interactions of the plasmaproducts after they transfer through the second planar electrode towardthe process chamber.
 2. The plasma processing system of claim 1, each ofthe two processing units further comprising: a planar diffuser betweenthe second planar electrode and the processing region, that allows theplasma products to transfer from the second planar electrode, throughperforations of the diffuser, into the processing region, the perforateddiffuser forming gas channels having outlets only on a processing regionside thereof, the outlets being interspersed with the perforations, suchthat an additional gas from the outlets can mix with the plasma productsas the plasma products enter the processing region.
 3. The plasmaprocessing system of claim 1, wherein the power supplies for the twoprocessing units are independently operable such that a plasma can existin the plasma generation chamber of one of the two processing units,while no plasma exists in the plasma generation chamber of the other ofthe two processing units.
 4. The plasma processing system of claim 1,further comprising an optical emission spectrometer configured toreceive the optical signal and to generate emission peak data from theoptical signal.
 5. The plasma processing system of claim 4, furthercomprising a computer configured for generating records of the emissionpeak data for at least one of the two processing units.
 6. The plasmaprocessing system of claim 5, wherein the computer is configured to:calculate a stability metric from the records of the emission peak datafor the one of the two processing units, over sequential processsequences of the plasma processing system.
 7. The plasma processingsystem of claim 6, wherein the computer is configured to: generate therecords of the emission peak data over a predetermined number of recipecycles; calculate the stability metric from the records generated overthe predetermined number of recipe cycles; and compare the stabilitymetric calculated from the records gathered over the predeterminednumber of recipe cycles, with a predetermined criterion, to assesssurface conditioning of the plasma generation region of the one of thetwo processing units.
 8. The plasma processing system of claim 1,wherein the insulator comprises ceramic and defines the port.
 9. Theplasma processing system of claim 8, wherein the ceramic forms a radialaperture that is configured to allow passage of optical emissions fromthe plasma therethrough, and the port comprises a fixture that positionsa fiber optic configured to capture the optical emissions, to form theoptical signal.
 10. The plasma processing system of claim 9, wherein theport further comprises an optical window formed of sapphire or quartz,the optical window being sealed to the ceramic, and disposed between theplasma and the fiber optic, so that the optical emissions can propagatefrom the plasma, through the optical window, and into the fiber optic.11. The plasma processing system of claim 1, wherein, for at least oneof the two processing units: the optical signal is captured by a firstoptical probe; the processing unit is configured to process a workpiecein the processing region; the processing unit is configured to performat least an etch recipe; and the processing unit is configured tocontrol the etch recipe with an endpoint detector responsive toemissions captured by a second optical probe, wherein the second opticalprobe is configured to monitor optical emissions that are affected byinteraction of a plasma with the workpiece.
 12. The plasma processingsystem of claim 1, wherein the source gases are second source gases, thesystem further comprising a remote plasma system configured to ionizefirst source gases, and the processing units are configured to receiveionized first source gases from the remote plasma system.
 13. A plasmasystem, comprising: a ring insulator defining an optical port, the ringinsulator comprising an insulating material formed in an annular shapethat is characterized by: an inner surface, an outer surface, a planarupper surface, and a planar lower surface; wherein the ring insulator isconfigured to radially define a cavity, and wherein the ring insulatordefines an aperture extending from the inner surface to the outersurface of the insulating material, substantially parallel with theplanar upper surface and the planar lower surface; an optical window,comprising an insulating material and disposed across the aperture; anda mounting block coupled with the ring insulator to retain the opticalwindow across the aperture, the mounting block configured to position anoptical fiber to allow optical emissions originating within the cavityto propagate through the optical window and into the optical fiber. 14.The optical port of claim 13, wherein: the ring insulator, the aperture,and the mounting block are configured to limit optical emissions thatcan reach the optical window to be optical emissions originating withinthe cavity.
 15. The plasma system of claim 13, wherein the mountingblock is configured to position a fiber optic connector with respect tothe optical window.
 16. The plasma system of claim 13, furthercomprising an o-ring sealing the optical window to the ring insulator,and wherein the outer surface of the ring insulator forms an annularrecess about the aperture, to accommodate the o-ring.
 17. The plasmasystem of claim 13, wherein the insulating material that forms the ringinsulator is ceramic.
 18. The plasma system of claim 13, wherein themounting block is coupled with the ring insulator by insulatingfixtures.